The core part of the existing gas water heater is a finned tube heat exchanger through which the high temperature gas flows through the fin side of the heat exchanger to heat the water inside the heat exchange coiler. The major heat transfer method takes the limited space heat transfer in the oxygen-free copper heat exchanger, and the high temperature smoke flows through the shell gap and the radiation and convective heat transfer in the limited space occur in the tube bundle. The velocity of flue gas is low. And it is usually laminar flow. The heat flux density is low, the heat can not be utilized sufficiently enough, which will result in a waste of energy. Although the addition of condensing heat exchangers at the flue gas outlet can further utilize a small amount of water vapor generated by flue gas combustion, the large temperature difference between the high temperature gas and heated water will result in irreversible loss, thus affecting the heat transfer efficiency.
In the gas water heater disclosed in U.S. Patent Publication No. US2007/0133963 A1, a closed vacuum chamber is used as a core heat transfer unit. The heat transfer coiler for heating the water is buried in the heat conduction particles in the cavity, and the heat conduction particles fill the entire enclosed chamber. The heat of the high temperature gas passes through the wall of the closed cavity in the form of heat conduction and then heat is conducted into heat conduction particles in vacuum and dry condition within the enclosed cavity, relying on the vibration of the particles, the ability of heat conduction is enhanced.